1. Field of the Invention
The present invention relates to a method and an apparatus for detecting materials put in a container such as an envelope and a plastic bag without breaking the container.
2. Description of the Related Art
Conventionally, an X-ray scanner and a sniffer dog are used for detecting specific materials including banned drug such as a narcotic drug and a stimulant drug, and an explosive such as an RDX and a TNT.
The detecting method using an X-ray scanner and a dog is not advantageous because when opening of the mailed envelope is restricted, the specific materials cannot be detected even if the specific material is contained in the envelope.
Meanwhile, References 1, 2 and 3 (Japanese Laid-Open Patent Publication Nos. 8-320254, 10-90174 and 2001-66375) propose apparatuses that use a tera-hertz wave to detect foreign materials contained in an article without breaking the article.
However, the apparatuses of References 1, 2 and 3 can only detect whether or not foreign materials exist. In addition, these apparatus output an displayed image, so that an operator needs to judge whether the foreign materials exist or not by watching the displayed image.
For this reason, when the operator becomes tired due to continuous watching, there is a risk that the operator misses the foreign material. Thus, the accurate detecting relies on a recognizing ability of the operator depending on concentration, experience, and intuition of the operator.